Antenna tuning system



April 2,8, 1959 I G. H. DEwl-rz ET AL 2,884,632

ANTENNA TUNING SYSTEM Filed Aug. 6, 1952 4 Sheets-Sheet 1 FIG. l.

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ANTENNA TUNING SYSTEM Filed Aug. 6, 1952 *Y 4.Sheets-Sheet 2 FIG. 4.

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G. HQDEWITZ ET AL ANTENNA TUNING SYSTEM 4 Sheets-Sheet 3 SOURCE SOURCE 0F 60A/7R01. CURRENT' 0- CONTROL v CURRENT*- soa/ecs op;

April 28, 1959 G. H. DEwlTz ET AL 2,884,632

ANTENNA TUNING SYSTEM Filed Aug. 6, 1952 Y 4 Sheets-Sheet 4 RE' o- SOURC INVENTORS C14/@L 6. SIVTHE/ME/P @SR/IARD. DEW/TZ "United States Patent ANTENNA TUNING SYSTEM Gerhard H. De Witz and Carl G. Sontheimer, Stamford, Conn.; said Sontheimer assignor to C.G.S. Laboratories, Incorporated, Stamford, Conn., a corporation of Connecticut Y Application August 6, 1952, Serial No. 302,962

11 Claims. (Cl. 343-850) 'Ihis invention is in connection with antenna systems incorporating electrically controllable inductance units. The invention is particularly useful where a single antenna system is used over a wide frequency range and the antenna is located remotely from the transmitter or receiver; the tuning and matching adjustments of the controllable inductor are done `electrically and require no moving mechanical parts.

In radio systems of this type, the efficiency of operation and the operating characteristics are affected adversely by improper impedance relationships between the transmission line and the antenna and between the transmitter and the transmission line. It is not diicult to secure the desired impedance relationships over narrow frequency ranges or in locations where adequate room for the antenna is available. However, in aircraft and other installations it is desirable for reasons of economy of space and weight to use a single antenna system and its feedline over the widest possible frequency range and to keep the physical dimensions of the antenna structure as small as possible.

Such antennas usually have a large reactance component and low radiation resistance. The reactance of the antenna can be overcome by the addition of compensating reactance, and the antenna impedance can be matched to the feedline by a suitable impedance matching network.

If xedmatching networks and tuning elements are used, good operation is usually achieved only over a relatively narrow range of frequencies.

Moreover, to be effective, such matching networks and tuning elements usually must be located at the center of the antenna if it is a dipole or at the base of the antenna if it is a grounded wire. This makes it impractical in most instances to increase the operating range by the use of multiple fixed control elements with selective switching arrangements or by the use of mechanically variable elements requiring as they do the use of complicated control devices for mechanically adjusting the remote lmatching networks and tuning elements.

The present invention provides a compact efficient and relatively simple remotely-controlled arrangement which permits minimum antenna dimensions and maximum operating frequency range.

A preferred embodiment of the invention provides for automatic or remote manual tuning of the antenna system without the use of mechanically moving parts at the antenna; the tuning system operating at high frequencies, over a wide frequency range, and with high etliciency. The system provides for maintaining a desired impedance compensation of the antenna, and/or a desired impedance match between the transmission line and the antenna and possibly a desired impedance transformation between the transmission line and the transmitter output. The system is also useful in the suppression of harmonics or other undesired signals. Another aspect of this invention permits these impedance relationships to be controlled remotely and automatically according to any one or more of several optimum criteria such as maximum radiated power, minimum reflected energy, etc. In another aspect of this invention, electromagnetically controllable inductors adjust lthe phase of currents in individual antennas utilized in an array, whereby the polarization or shape or direction of the directive pattern of emission is influenced. Furthermore, the invention may be used where relative output or input levels of two antennas are alternately or independently controlled as for example in some types of diversity receiving or transmitting systems. In that case, only the desired antenna is tuned to optimum conditions, whereas the other is deliberately detuned and made substantially inoperative.

Under most conditions, antenna systems can be considered to be reversible in accordance with the terms of the well-known reciprocity theorem. Therefore, it is to be understood that reference to the transmission of energy and transmitting apparatus also embraces corresponding reception of energy and receiving apparatus, thus simplifying the explanation of the invention.

The foregoing objects, aspects, and advantages of the invention will be in part pointed out and in part apparent from the following description considered in conjunction with the accompanying drawings, in which:

Figure l is a diagrammatic representation of a remotely-tuned dipole antenna system utilizing a controllable impedance transformer coupling at the junction of the antenna and the transmission line;

Figure 2 is an enlarged perspective view of a controllable inductor useful in the circuit of Figure 1;

Figure 3 diagrammatically shows a remotely tuned antenna system in which the tuning is continuous and entirely automatic;

Figure 4 is a perspective view of a variable inductor suitable for use in the circuit of Figure 3;

Figures 5, 6, 7 and 8 show other systems for remotely tuning the antenna element; and

Figures 9, lO and l1 are diagrammatic representations of various antenna tuning and filter arrangements.

Figure l shows a transmitting system in which radio signals from a transmitter 2 are radiated by a remotelypositioned dipole antenna 4. The signals are fed from the transmitter 2 to the antenna structure through a transmission line or cable 6 which, for example, may be an open wire line or a coaxial cable. The signal from this line is coupled to the antenna through a variableimpedance transformer 8, which also insertsv an inductive reactance, whose magnitude is controllable, that compensates for the capacitive reactance of the antenna.

This transformer includes a core 10 of ferromagnetic material carrying a control winding 12 and two signal windings 14 and 16. The control winding is connected to a source 18 of direct current which flows through the control winding 12 and partially saturates the core 10 and thereby varies the inductance of the signal windings 14 and 16. A potentiometer 20 is arranged to regulate either manually or automatically the magnitude of this current so that as the operating frequency of the system is changed, the changes in control current provide the optimum value of antenna compensating reactance at these various operating frequencies.

Figure 2 shows the physical construction of the controllable impedance device 8. To isolate the control winding 12 from the radio frequency alternating signals of the signal windings 14 and 16, the latter windings are each divided into two equal series-connected portions, as indicated at 141 and 14-2 and 16-1 and 16-2, respectively, which are wound through an opening 23 and around opposite rim portions of the ring-shaped core 10. The individual portions of the windings 14 and 16 are each connected in such direction that the 3 alternating magnetic flux'lines induced in the core encircle the opening 23 and do not link with the control winding 12. The two windings 14 and 16 are interwound to insure close coupling at all times.

With this arrangement, the antenna can be tuned for each frequency of operation by`varying the D.C. control current in thewinding 12. For example, 4as this control curr/ent is'increas'ed, the magnetic saturation `of the core increases, thus reducing the reactive impedance of the signal windings 14 and 16. The slidable connection of the'potentiometer 20 can be adjusted manually each time the frequency of operation is changed to produce the optimum impedance relationship or any desired automatic control circuit or device may beutilized to control the current through the winding 12. n

In order to permit high frequency operation without prohibitive losses in power, the co-re 1t? preferably is formed of ferromagnetic ceramic material such as is described by Snoeck in U.S. Patents 2,452,529; 2,452,530; and 2,452,531. rl'his material maintains a high Q even when subjected to substantial magnetic saturation and also provides a very wide range of inductance variation.

As an alternative arrangement in place ofthe controllable impedance transformer as shown, the winding 14 may be omitted and the line 6 can be tapped into the winding 16 at balanced points equidistant from the ends ofthe winding 16 so that this winding acts in effect as an aiuto-transformer winding of controllable impedance for coupling the line and antenna. With this latter arrangement the winding 14 `may be included for the purpose of providing a tuned lter to remove undesired harmonics from the system. Thus, a condenser is connected across the winding 14 and is proportioned to resonate with the winding 14 at the harmonic frequency which is desired to be excluded. As the control current through winding 12 is changed for different operating frequencies, the resonant frequency of the winding 14 and condenser changes so that it follows the changes in operating frequency and continues to remove the undesired harmonics of the operating frequency.

In certain instances, parts performing generally corresponding functions and appearing in different figures of the drawings are referred to by the same numbers followed by different letters.

Figure 3 shows a stub-type antenna 26 which'projects from ka ground conductor 28, which, for example, may be the metallic covering of an aircraft or a portion of the hull of a ship, or the like. Radio frequency energy from the source 2a is fed to the antenna through the transmission line 6a and an automatically-controlled antenna tuning section 30. This tuning network utilizes two controllable inductors 31 and 32 which permit separate and independent control of the antenna compensating reactance and the impedance transformation between the antenna k26 and the transmission line 6a.

The signal windings 34 and 35 of the inductors 31 and 32, respectively, are connected in series with the stub antenna 26 andl in conjunction with a shunt condenser 36 to form a T-section network. The principles of the automatic control system indicated diagrammatically in Figure 3 are set forth in a copending application of Carl G. Sontheimer, Serial No. 781,834, filed October 27, 1947, now U.S. Patent No. 2,61l,030. In order to detect the electrical conditions along the transmission line 6a, a detection unit 37 is connected to the line 6a near the source 2a, and is yconnected to automatic control equipment, generally indicated at 38, which is used to cont-rol the antenna tuning inductors 31 and 32.

A source 18a of direct current is connected to supply current to the control windings 40 and 41 of the controllable inductors 31 an'd 32. A potentiometer 42 connected to the output of the source 18a provides an adjustable Voltage that is( connected through a line 43 and the common ground circuit to thecontrol winding '40.

4 A similar potentiometer 44 provides an independently adjustable voltage forthe control winding 41 through' a line 45.

Periodic variations in the control current through the windings 40 and 41 are produced by continually varying variable resistors 46 and 48, respectively, connected in series with the lines 43 and 45 and ganged mechanically to a control unit 49. The resulting changes in the tuning adjustment of the antenna 26 produce corresponding variations at the detection unit 37 which in turn actuate the control unit 49 so as toV produce and maintain the proper adjustments of the main control potentiometers 42 and 44. Reference is made to the above-identified Sontheimer application for a more complete disclosure of the automatic control feature.

1t will be clear, however, that the impedance-matching relationship and the antenna compensating reactance can be adjusted `separately and independently even though each of the inductors 31 and 32 will affect both conditions.

With a T-section of this type, the impedance transformation between the base of the antenna 26 andthe adjacent end of the transmission line 6a is a function of the ratio of the inductances lof the signal windings 34 and 35 while the reactance at either of these points is a function of the sum of these inductances. Hence, the impedance match therebetween and the reactance at either or" these points can be separately controlled to produce the optimum operating condition, for example maximum radiated power, or minimum reiiected energy and standing wave ratio, or maximum efficiency.

The inductors 31 and 32 are each generally similar'to the variable impedance matching transformer 8 (see Fgure 2), except that they have only a single signal winding 34 and 35, respectively, which are each divided into two portions, wound through a slot (not shown in Figure 3) and connected in such directions as to cle-couple them from the control windings 4t) and 41, respectively, ina manner similar to either winding 14 or 16.

These periodic variations in the tuningadjustment of the antenna 26 can be provided in a variety of ways, for example, Figure 4 shows a variable inductor 56 which may be used in an alternative arrangement of the system shown in Figure 3. The inductor 56 includes a core 58,'a control winding 60 and the signal winding 62, which for example corresponds with either'of the signal windings 42 or 44 of the variable inductors 31 and 32 shownin Figure 3. Additionally, an auxiliary control winding'64 for providing these periodic Variations is woundon the core as shown. A pair of such inductors can be incorporated into a tuning section, such as the sectionO, and periodic variations in the auxiliary control currents, which, for example, may be provided by a pair of auxiliary potentiometers connected to the source'18a, are sent through the auxiliary control windings.

The antenna tuning system of Figure "5 is similar tothe one shown in Figure 3, except that the aultomatic'control equipment is omitted, and the tuning section J30b is arranged as a ar-section. The signal windings l34band 35h of the variable inductors 31b and 32b are connected in shunt with the transmission line 6b near the base of the antenna 26b, and the condenser 36b is connected in series with the antenna and its feedline. As discussed above, the impedance transformation'and the antenna compensating reactance can be separately controlled fby the magnitudes of the D.C. currents owing from the source 18b through the leads 43b and 45b as determined by the adjustment of the potentiometers 42b and 44'b During operation, these potentiometers are manually or automatically adjusted to provide optimum antenna compensalting reactance and impedance match between the antenna and line 6b. l

The antenna tuning system of Figure 6 is 'similar to Figure l5 except that the tuning section 66 includesf'a `cr'itrollable inductor''having a signal winding'69 in series with the feedline 6C and a controllable inductor 70 having a signal winding 71 shunted across this line. A tuning condenser 72 may be connected in shunt across the line 6C between the base of the antenna 26o and the ground conductor 28C. The inductance of these windings 69 and 71 are separately controlled by the magnitudes of the D.C. control currents from the source 18C adjusted by the potentiometers 42o and 44e and fed through the leads 43e and 45C to the control windings 74Y and 76. With this arrangement, the impedance matching relationships between the antenna 26C and the line 6c; and also the antenna-compensating reactance can each be separately adjusted either manually or automatically to provide optimum operating characteristics. In Figure 6 the shunt winding 71 is connected to the transmitter side of the series winding 69, an alternative arrangement which also provides separate and independent control of the impedance match and compensating reactance is to connect winding 71 on the opposite side ofthe winding 69.

. Figure 7 shows a balanced remote antenna tuning system suitable for dipoles and other balanced antenna elements. The two poles of the dipole antenna 82 are connected to opposite sides of the transmission line 6d through the signal windings 84 and 86 of variable inductors 88 and 90. These windings 84 and 86 serve to introduce antenna-compensating inductance in series with each side of the line 6d, and the value of this inductance controlled by the currents through each of the control windings 92 and 94, respectively, to produce the desired optimum conditions within the system depending upon the. desired operating characteristics. For example, the antenna compensating inductance of windings 84 and 86 maybe adjusted to equal values for producing the same phase relationships in both elements of the dipole, or the phases of the two elements can be varied by regulating the inductances of the windings 84 and 86 to different values in order to change the directivity of the antenna. Also, the relative output (or input) from each of the elements of the antenna 82 can be alternately or independently controlled by the variable inductors 88 and 90. v The system shown in Figure 8 controls the reactance component at both ends of the transmission line to produce optimum conditions in both places. In order to provide the antenna-compensating reactance, the signal winding 92 of the variable inductor 94 is connected in series with the ungrounded side of the transmission line 6e near the base of the stub antenna 26e. The inductance of the winding 92 is controlled by the magnitude of the D.`C. current, which is adjusted by the potentiometer 44e and'sent through the control winding 94. It is adjusted to produce optimum antenna compensating reactance. M the transmitter end of the line, a similar inductor 95 has its signal winding 96 connected in series with the transmission line 4e. Its inductance is controlled by the magnitude of the current flowing through the control winding 97, which is adjusted by the setting of the potentiometer 42e to provide an optimum value of reactance presented by the transmission line to the transinitter 2e.

Figures 9 and l0 show alternative remotely controlled antenna tuning and filter systems, in which the signal windings 100f and 100g of the variable inductors 108]" and 108g insert series inductance of controlled value into-the transmission lines f and 6g near the base of the antenna 26jc and 26g. The values of the antennacompensating industances, which are inserted in series with the lines 6f and 6g, are controlled by the currents flowing from the sources 18f and 18g through the potentiometers 104) and 104g and along the lines 106]c and 106g through the control windings 10Sf and 108g, respectively, and may be manually or automatically adjusted to optimum values. In Figure 9, this control cur- Aet also regulates the setting of a tuned filter circuit `I09f connected from the base of the antenna element 267 to ground. This filter circuit includes the variallet inductance signal winding i connected to ground through a condenser 1121. By setting the value of the fixed condenser 112]c so that this filter circuit is in series resonance at a predetermined harmonic of the signal, this harmonic is filtered from the system both during transmission and reception. When the control current is changed to alter the reactance loading of the line for antenna compensation at different operating frequencies, this same change in current affects the control winding 114f of the variable inductor 116f and hence changes the inductance of the winding 110f to retune the filter 109i to the same harmonic of the new operating frequency. Thus, the filter 109]c tracks the operating frequency and suppresses a predetermined harmonic in the system irrespective of variations in the operating frequency.

An alternative filter arrangement may be used wherein the inductor 116]c is replaced =by an inductor of the general form shown in Figure 2 with one of the signal windings thereof being connected between the base of thel antenna and ground and the other winding is connected to opposite terminals of the condenser 1121.

In Figure 10, the filter circuit 109g includes the condenser 112g connected in parallel with the variable inductance winding 110g, and both being connected in series with the transmission line 6g. Thisy parallel filter combination 109g is rtuned to be at resonance to present a high impedance at the frequency of the harmonic which is desired to be excluded from the system. The magnitude of the control current through the control winding 102g regulates the antenna-compensating inductance in series with the line 6g and also controls the inductance of the winding 110g to cause the filter 109g to track the operating frequency in a manner similar to the system shown in Figure 9.

An alternative filter arrangement may be used wherein the inductor 114g is replaced by an inductor of the general form shown in Figure 2 with one of the signal windings transmission line 6h. This filter 120 is tuned to block any` frequency components significantly above the frequency of the desired transmitted signals. The filter and the antenna reactance compensating inductor 122 are controlled by the magnitude of a D.C. current flowing from the source 18h over the line 124 so that they track each other through vario-us operating frequency ranges. Thus, the filter is always properly tuned to block undesired frequency components above the signal frequencies being used. The filter comprises a pair of variable inductors 126 and 128 with their signal windings 130 and 132 connected in series with each other and with the line 6h and a condenser 134 shunted across the line 6h at their junction. A resistor 136 may be shunted across the transmission line between the T-section filter and the antennacompensating inductance 121.

The controllable inductors incorporated into the systems shown in Figures S through l1 are generally similar to the inductors 31 and 32 shown in Figure 3. For example, these inductors may be similar to the inductor 56 shown in Figure 4, except that the auxiliary Winding 64 is omitted. It is to be understood that the principles set forth above in connection with controllable inductors having single cores apply equally Well to multiple core structures. For example, each controllable inductor may comprise a pair of cores with control and signal windings thereon, With at least one of said windings being formed in two sections of turns. A section is placed on each' core, and they are connected in series in such direction that the flux from the other winding links each of said sections of turns in opposite directions. Thus, the windings areisolated from each other and' have no net efectivemutual ux linkages; however, `one of these windings is used to control the inductance of the other winding by regulating the degree of magneticsaturation of the cores.

In the various arrangements shown, additional circuit elements may be used where required. For example, Xed transformers may be added either between the transmission` line and the controllable impedance device or betweenrthe antenna and this device, condensers or inductors may be connected to the line or used in various tuned harmonic traps, etc.

Various remotely controllable antenna tuning systems, some including filter arrangements, have been described, and from this description it will be apparent that antenna tuning systems embodying the present invention are well adapted to attain the ends and objects set forth herein and that the various embodiments of the invention shown herein can be modied so as to produce operating char# acteristics bes-t suited to the needs of each particular use. Moreover, in certain more critical applications, the range or stability of the variable inductance units may be increased by equipment as is described in the applications of William D. Gabor, Serial No. 234,581, filed June 30, 1951, now Patent No. 2,755,446, and Serial No. 279,825, tiled April l, 1952, now abandoned.

We claim:

l. An antenna tuning system comprising an antenna unit, a radio transmitter unit, an energy transmission line for conveying radio signals between said transmitter and said antenna unit, a controllable inductor having a core of ferromagnetic material with a control winding and a signal winding wound on said core, said control winding being substantially isolated from the signals in said signal winding, the inductance of said signal winding being controlled by the current through said control winding, said signal winding being connected to said transmission line near said antenna to control the impedance presented to said line by said antenna, a source of control current near said transmitter, means for varying said current, a conductor between said -current varying means and said control winding for conveying control current to said winding, a detection unit connected to said line near said transmitter for sensing the conditions `on said line, and a condition-responsive control connected to said detection unit and arranged to control said current varying means.

2. An antenna tuning sys-tem comprising a ground conductor, a stub type antenna projecting from said ground conductor, fa source of radio frequency for energizing said antenna, an energy transmission line extending between said source and said antenna, an electrically controllable inductor positioned near the base of said antenna, said inductor having a core of ferromagne-tic material, a signal winding on said core, a control winding on said core for varying the degree of magnetic saturation thereof in accordance with variations in control current flowing through it, said control winding being substantially isolated from said signal winding, the inductance of :said signal winding being controlled by this saturation, said signal winding being connected to said transmission line near the base of said antenna to control the impedance relationships between said antenna and said transmission line, a source of D.C. control current near said radio frequency source, conductor means extending from said current source to said control winding, and control means near said sources for varying said control current, whereby said impedance relationships can be remotely controlled by varying the current through said control winding.

3. An antenna tuning system comprising a ground conducto-r, a stub type antenna projecting from said ground conductor, a source of radio frequency for energizing said antenna, an energy transmission line extending between said source and said antenna, an antenna tuning section position near the base of said antenna, said section including a pair of electrically controllable induc'tors and a condenser connected to said transmission line near the base of said antenna, each of said inductors having a core of ferromagnetic material,y a signal Wind-.-

ing on said core and connected to said transmission. line, near the base of said antenna, and a control windingl on said core for varying the degree of magnetic saturation thereof in accordance with variations in a control current owing through it, the inductance of said signal winding being controlled by this saturation, each of said control windings being substantially isolated from the signal` winding on its respective core, a source of directr control` current near said radio frequency source, a conductor extending from said current source to each of said control windings, and means near said sources for separately varying the contro-l currents through each of the control windings, whereby the impedance matchingy relationship between said antenna and the line andl the reactance. presented to the end of the line near said antenna caribe. remotely and separately controlled by varying the currents through said control windings.

4. An antenna tuning system as claimed in claiml 3,. and wherein said antenna tuning section is a T-section having said signal windings connected in series with said transmission line` near the base of said antenna, and having said condenser connected across said transmis, sion line between Said signal windings.

5. An antenna tuning system comprising an antemta,l a radio transmitter unit, an energy transmission line, forl conveying radio signals between said transmitter and said antenna unit, an antenna tuning section positioned near said antenna, said section including a pair of electrically variable inductors, each of said inductors having a core. of ferromagnetic material with a control winding and a signal winding wound on said core, said control winding being substantially isolated from the signals in said signal winding, the inductance of each of said signal windings being controlled by the current through the control winding on the same respective core,v each of said signal windings being connected to said transmission line near saidY antenna to control the impedance match between said line and said antenna and the reactance presented to said line by said antenna, a source of control current near saidv transmitter, main control means for adjusting said control current, auxiliary control means arranged to cyclicallyy and separately vary the saturation of said cores by relatively small amounts, a conductor between said control means and each of said control windings for conveying control currents to said windings, a detection unit connected to said line near said transmitter for sensing the changing conditions on said line produced by said cyclic variations and a condition-responsive control connected to said detection unit and arranged to control said main control means to maintain optimum an impedance match between said line and said antenna unit and valso an optimum reactance at the end of said line near said antenna.

6. In a system for transmitting or receiving radio energy over a wide range of frequencies wherein the antenna is positioned remotely from the transmitter and is coupled thereto by an energy transmission line and wherein the antenna is utilized over said wide range of frequencies, an antenna tuning and matching system comprising 'an antenna, a transmitter, an energy ltransmission 'line for conveying radio energy over said wide range 'of frequencies between said transmitter and said antenna, at least two controllable inductors each including a ferromagnetic core having thereon a control winding and a signal winding, said signal and control windings in each induc'tor being substantially isolated from each other, each of said signal windings being connected to the 'transmission line near the antenna, a source of direct control current connected to each of said control windings, each of said control windings being arranged to vary the degree of magnetic saturation in its respective 'associated core in response to the magnitude of the control current therein, thereby to vary the inductive reactance of its associated signal winding, and control means arranged to regulate the magnitude of the control current in each of said control windings, whereby said variable inductors provide a wide range in inductive reactance to compensate for the reactance of said antenna over said wide range of frequencies and to match said antenna to said transmission line over said wide range of frequencies.

7. An antenna tuning system comprising an antenna unit, a radio transmitter unit, an energy transmission line for conveying radio signals between said transmitter and said antenna unit, a lirst controllable inductor having a core of ferromagnetic material, a control winding, and a signal winding wound on said core, said control winding being substantially isolated from the signals in said signal winding, the inductance of said signal winding being controlled by the current through said control winding, said signal winding being connected to said transmission line near said antenna to control the impedance presented to said line by said antenna, a second controllable inductor having a second core of ferromagnetic material, a second control winding, and a second signal winding Wound on said core, the inductance of said second signal winding being controlled by the current through said second control winding, said second signal winding being connected to said transmission line, a source of control current, means for varying said current, conductor means between said current varying means and said control windings for conveying control current to said control windings, a detection unit connected to said line near said transmitter for sensing the conditions on said line, and a conditionresponsive control connected to said detection unit and arranged to control said current varying means.

8. An antenna tuning system comprising an antenna unit, a radio transmitter unit, an energy transmission line for conveying radio signals between said transmitter and said antenna unit, first and second controllable inductors each having a core of ferromagnetic material with a control winding and a signal winding wound thereon, each of said control windings being substantially isolated from the signals in said signal windings, the inductances of said signal windings being controlled by the current through said control winding, both of said signal windings being connected to said transmission line near said antenna to control the impedance presented to said line by said antenna, a condenser connected to said transmission line adjacent said signal windings, a source of control current, means for varying said current, conductor means between said current varying means and said control windings for conveying control currents to said control windings, a detection unit connected to said line near transmitter for sensing the conditions on said line, and a condition-responsive control connected to said detection unit and arranged to control said current varying means.

9. An antenna tuning system and harmonic lter means tracking therewith comprising an antenna unit, a radio unit, an energy transmission line for conveying radio signals between said radio unit and said antenna unit, a rst controllable inductor having a core of ferromagnetic material, a control winding, and a signal winding Wound on said core, said control winding being substantially isolated from the signals in said signal winding, the inductance of said signal winding being controlled by the current through said control winding, said signal winding being connected to said transmission line near said antenna to control the impedance presented to said line by said antenna, a second controllable inductor having a second core of ferromagnetic material, a second control winding, and a second signal winding wound on said core, the inductance of said second signal Winding being controlled by the current through said second control winding, a condenser, said second signal Winding and said condenser forming harmonic lter means and being connected to said transmission line, a source of control current, means for varying said current, conductor means between said current varying means and said control windings for conveying control current to said control windings, said current varying means simultaneously changing the inductance of said rst and second signal windings, thereby to track said harmonic filter means with said rst signal winding, a detection unit connected to said line near said radio unit for sensing the conditions on said line, and a condition-responsive control connected to said detection unit and arranged to control said current varying means.

10. An antenna tuning system as claimed in claim 3 and wherein said antenna tuning section is a 1r-section having each of said signal windings connected across said transmission line near the base of said antenna, and having said condenser connected in series with said transmission line between adjacent terminals of said signal windings.

l1. An antenna tuning and lter system for operation over a wide frequency range comprising a ground conductor, a stub-type antenna projecting from said ground conductor, a source of radio frequency for energizing said antenna, an energy transmission line extending between said source and said antenna, an antenna reactance compensating electrically variable inductor and a filter section positioned near the base of said antenna, said section also including rst and second electrically Variable inductors and a condenser, each of said inductors having a core of ferromagnetic material, a signal winding on each of said cores and a control winding on each of said cores for Varying the degree of magnetic saturation of its respective core in accordance with variations in a control current flowing through it, the inductance of each of said signal windings being controlled by this saturation of its respective core, each of said control windings being substantially isolated from the signal winding on its respective core, the signal Winding of said antenna compensating inductor being connected to said transmission line near said antenna, the signal windings of said rst and second inductors being connected in ladder tuned filter circuit with said condenser, said tuned circuit being connected in series with said line and arranged to filter undesired frequencies from said line, a source of direct control current near said radio frequency source, conductive means extending from said current source to each of said control windings, and control means near said sources arranged to regulate the control current flowing through each of said control windings, whereby said antenna compensating inductor can be remotely controlled by said control means to produce optimum reactance at the end of said line near said antenna, and said iilter section can be remotely controlled by said control means to filter out undesired signals, and whereby said reactance compensation and said ilter track each other as the operating frequency of said system is changed.

References Cited in the iile of this patent UNITED STATES PATENTS 1,684,235 Love Sept. 1l, 1928 1,819,904 Love Aug. 18, 1931 2,200,263 de Kramolin May 14, 1940 2,581,348 Bailey Jan. 8, 1952 2,611,030 Sontheimer Sept. 16, 1952 OTHER REFERENCES The Wireless World, Mar. 3, 1938, pages 186-188. Radio Craft, July 1939, page 13. Proceedings of the IRE, April 1938, pp. 439, 440. 

